Senate backers of an immigration overhaul kept the bill alive Tuesday, setting up debate and votes likely to determine the fate of the legislation in the 110th Congress.

But even after losing a key procedural vote, opponents of the bill refused to go away quietly, stalling consideration of a series of amendments by insisting the clerk read aloud a 373-page amendment.

That amendment encompasses 27 proposed changes to the bill the Senate will consider this week, which has often appeared near death only to be resurrected over the past few weeks.

The opponents’ tactics did not pose a new threat to the bill’s well-being. Instead, Republicans Jim DeMint of South Carolina, Tom Coburn of Oklahoma and their allies appeared to be engaged in an effort to thwart action.

Enough senators appeared game to see where the final slate of amendments would take the measure after voting, 64-35, earlier in the day to limit debate on a motion to proceed to the bill (S 1639).

Yet even with more than 60 senators agreeing to debate the bill, its prospects were far from certain.

“This was a vote to proceed to consider these other amendments,” said New Mexico Democrat Jeff Bingaman. “I don’t know how I will vote on final passage.”

And, despite the best efforts of the opponents, that vote is coming soon.

Majority Leader Harry Reid, D-Nev., filed a motion to end debate on the bill, setting up a decisive cloture vote Thursday. If that fails, the immigration overhaul could be lost for this Congress.But if it prevails, Senate passage is expected Friday.

Knowing he faced a crafty opposition, Reid broke out a rarely used procedural tactic known as a “clay pigeon,” designed to speed up the process and dilute the power of the minority.

But Reid couldn’t neutralize the bill’s opponents altogether.

When he made the routine motion to waive the reading of the amendment, DeMint objected. So Kathleen Alvarez, the assistant legislative clerk, began crisply reading every line of the document on the Senate floor at 5:44 p.m.

Within 20 minutes, the majority whip’s office sent out an e-mail announcing no further roll call votes for the day.

Feeling the point was made, the sides agreed to dispense with the reading at about 6:30 and start fresh with votes on Wednesday.

The procedural jousting could be the least of the hurdles faced by the measure’s supporters.

A number of senators on both sides of the aisle have criticized various aspects of the legislation — with the common thread being a lot of dissatisfied senators who want to change the bill.

Some said they agreed to bring the measure back only to have a chance to see how the amendments shake out.

Even a key booster indicated Tuesday that his vote was not guaranteed.

South Carolina’s Lindsey Graham, a Republican negotiator of the compromise legislation, said he would withdraw his support if the chamber fails to adopt one of the amendments he has offered. Graham’s proposal would require at least all illegal immigrants’ heads of households to “touchback” in their country of origin within three years of the bill’s enactment and before they receive Z visas that enable them to stay indefinitely in the United States.

His proposal was an alternative to an amendment by Kay Bailey Hutchison, R-Texas, that would require all adult illegal immigrants to return home within two years.

The underlying bill would require heads of households to return home only if they want to become legal permanent residents.

Graham’s amendment — part of a broadly drafted enforcement proposal he has offered with Republicans Jon Kyl of Arizona and Mel Martinez of Florida — is an attempt to sway GOP doubters who say the bill is too weak on enforcement.

Graham said his position to back away from the bill if the amendment is not adopted should not be interpreted as speaking for the coalition of senators, the so-called gang of 12, that put the bill together.

“That means Lindsey Graham won’t vote for it,” he said. “What I have tried to do is put together an amendment at the end to address legitimate constructive criticism that will make this bill much stronger in the enforcement arena.”

Majority Whip Richard J. Durbin, D-Ill., said many Democrats believe the touchback proposal goes too far.

But Graham appeared to have the backing of one important member of the majority.

“I can live with that,” said Massachusetts Democrat Edward M. Kennedy, the sponsor of the legislation.

Another potential deal-breaker is a proposal from Charles E. Grassley of Iowa, the ranking Republican on the Senate Finance Committee, that would strike a core provision in the bill — the employer verification system — and replace it with a less stringent alternative.

The Grassley amendment, cosponsored by Democrats Max Baucus of Montana, chairman of the Finance Committee, and Barack Obama of Illinois, would not require the verification of current employees unless there is evidence to suspect unlawful employment.

That distinction, among others in the alternative, has drawn sharp criticism from Homeland Security Secretary Michael Chertoff.

“That doesn’t pass the common sense test,” Chertoff said in a conference call with reporters Tuesday, adding that he’s “confident” that it will not be adopted.

A Senate Finance Committee aide called it “bizarre” to verify all employees with the goal of finding illegal workers when the “purpose” of the legislation “is to make all illegal workers legal.”

House Republicans were so determined to go on record in opposition to the Senate bill, they held a meeting to vote on an official denouncement.

Members met for an hour behind closed doors, emerging after a symbolic 114-23 vote intended to underscore the House GOP conference’s opposition to the Senate legislation.

“This shows that 85 to 90 percent of Republicans are against amnesty, which is what the Senate bill has become,” said Patrick T. McHenry, R-N.C. “It’s a clear message at the right time.”

Republicans made the move following a weekly meeting between House and Senate GOP leaders and President Bush.

House Minority Leader John A. Boehner, R-Ohio, said he informed Bush of the impending vote in the conference.

Bush, Boehner added, “said ‘I understand.’ ”

Some Republicans, including Rep. Jeff Flake of Arizona, opposed the vote and said it was wrong to come out against a bill the Senate has yet to act on.

But Boehner said no one in the meeting spoke out in favor of the Senate measure. Instead, Boehner said, “most of the 23 were those concerned with the process we were going through.”

The motion was introduced by Peter Hoekstra, R-Mich.

“Border security, enforce the laws — that is the message we are sending forward,” Hoekstra said.

Susan Ferrechio contributed to this story.